The present invention relates to the inclusion in a digital wristwatch, of a chronograph, a voltage, frequency and period measurement device, and a wrist calculator into one package. Current engineering art provides a digital wristwatch, using liquid crystal displays, quartz oscillator, and using complementary metal oxide field effect semiconductor logic techniques to divide the quartz oscillator frequency, typically 32,768 Hz, down to a frequency of 1 Hz to advance the clock register of the watch. Additional similar logic is used to count the frequency down, to store the current time, and provide the liquid crystal displays with the necessary waveforms. A battery provides the necessary power source for the circuitry. Obviously, since the size of the battery and all circuitry and displays must fit inside the watchcase, power consumption must be kept at a minimum, and all possible circuitry must be placed on a single large scale integration integrated circuit. It is characteristic that complementary metal oxide field effect semiconductor logic devices draw nearly negligible current in the quiescent state, and draw appreciable current only while switching. It follows that a frequency divider, such as used in current art timekeeping circuitry, draws the larger amount of current in the higher frequency stages and almost negligible current in the low frequency stages. This phenomenon makes practical the inclusion of other desirable low frequency functions in a timekeeping device. It is known that economy may be achieved by multiplexing the functions performed by each circuit in the device, wherever possible.
It is known to selectively display some other function within a digital wristwatch. U.S. Pat. No. 3,757,509 issued Sept., 1973 to Fujita and U.S. Pat No. 3,795,099 issued March, 1974 to Tsuruishi both disclose a combination watch and chronograph with means to selectively display the contents of a memory register. U.S. Pat. No 3,803,834 issued April, 1974 to Reese discloses a combination wristwatch and calculator with means to couple either circuit to the display. Other combination devices are known in the art as well as digital display electronic timepieces with multiplexing features using integrated circuits as exemplified in U.S. Pat. No. 3,721,084 issued March, 1973 to Dargent. However these have been directed to displaying only alternate functions and the internal circuitry has been especially adapted to those functions rather than adapted to a multipurpose display capability.
There is need for a device to supplement the features of an electronic digital solid state watch with a plurality of additional functions. One such function may be a digital timer with selectable increments, such as hours, minutes, seconds, or tenths of seconds for measuring, for example, the speed of an automobile or a boat over a measured mile, for keeping track of the time on a parking meter, or for timing an industrial process or an athletic event.
A wrist calculator function may be provided which can perform various arithmetic functions such as recording expenditures in a supermarket, balancing a checkbook stub, or checking inventories.
A voltage, frequency, and period measuring device may be included, which can make voltage and frequency measurements on an externally applied signal and display the results of such measurement on the display on the face of the device. The device is thus capable of measuring pulse rates, temperatures (with the addition of simple external thermo-sensitive elements), or frequencies (such as tones produced by a musical instrument).
Accordingly one object of the invention is to provide an unique device which, in one form, can combine the function of a wristwatch, chronograph, wrist calculator and digital frequency, period and voltage meter.
Another object of the invention is to provide an electronic wristwatch which allows selective display of one of a plurality of information sources in compact form while enhancing the versatility of the various functions.